Small fuel cells design

The need for different and novel materials as possible DLs has increased substantially in the last few years—especially with the development of new and more complex fuel cell designs. Lurthermore, the interest in small-scale fuel cells to be used as battery replacements in portable electronic devices such as PDAs, laptops, cell phones, music players, etc. has pushed the research for irmovative, inexpensive, and efficient fuel cells further [72,73]. Therefore, it is not surprising that most of the recent new DL materials are being used in micro fuel cells. 

In order to study cathode flooding in small fuel cells for portable applications operated at ambient conditions, Tuber et al.81 designed a transparent cell that was only operated at low current densities and at room temperature. The experimental data was then used to confirm a mathematical model of a similar cell. Fig. 4 describes the schematic top and side view of this transparent fuel cell. The setup was placed between a base and a transparent cover plate. While the anodic base plate was fabricated of stainless steel, the cover plate was made up of plexiglass. A rib of stainless steel was inserted into a slot in the cover plate to obtain the necessary electrical connection. It was observed that clogging of flow channels by liquid water was a major cause for low cell performance. When the fuel cell operated at room temperature during startup and outdoor operation, a hydrophilic carbon paper turned out to be more effective compared with a hydrophobic one.81... 

The fuel eell reaction is exothermal therefore it generates heat as a by-product. To maintain the desired temperature, heat must be removed from the system. Some heat dissipates from the outer surface of the fuel cell and the rest must be taken away with a eooling system. The cooling medium may be air, water, or a special coolant. The inner design of the fuel cell must allow the coolant to pass through, for example, a coolant plate or coolant chaimel on the back of the anode or cathode plate. Small fuel cells need a heater to reach the operating temperature because so much heat is being taken away from the outer surface [1]. The heat balance within a fuel cell can be written as... 

Portable electronic devices need very low power for their operation, often milliwatts or at most a few watts, and no more than 10 W. Small low-power fuel cells designed as a power supply for portable devices are termed micro-fuel cells or mini-fuel cells (mini-FCs), the latter term being preferred. The concept of a miniamrization of fuel cells is also current. 

The traditional structure of a fuel battery is that of a vertical stack of alternating bipolar plates, MEAs, and heat-exchange plates that is compressed with the aid of massive end plates and tie bolts. This structure is poorly adapted for building mini-fuel plants. Particularly for the applications mentioned, special small fuel cells are needed that have design principles different from those of their large cousins. 

The importance of solving these problems increased during the last decade with the rising necessity to develop small fuel cell plants for portable devices and for electric vehicles, for which a reliable simplified and low-cost design is necessary (see Chapter 17). To circumvent these problems, numerous efforts have been made to use other, nonconventional principles in fuel ceU design. 

Numerous examples of small fuel cell-based power units produced and used for domestic applications could be cited. Thus, the Vaillant Group, which has production facilities in a number of European countries, has developed a combined heat and power unit (CHP unit) designed for an electric power output of 4.6 kW and a heat output of 11 kW. Such units were installed in several countries (Germany, the Netherlands, Spain, Portugal). The European Commission has supported 30% of the full project costs, estimated at 8.6 billion [Kommu-nalwirtschaft, No. 2, p. 107 (2004)]. 

The first edition of this book was published in December 2008. This second edition is updated with information published after this date up to October 2011. Two chapters of the first edition were rewritten Chapter 15 (modeling of fuel cells) and Chapter 14—now Chapter 17 (small fuel cells for portable devices). In this edition three new chapters of high current interest are also included Chapter 14 (structural and wetting properties of fuel cell components). Chapter 16 (experimental methods for fuel cell stacks), and Chapter 18 (nonconventional design principles for fuel cells). 

The first is a small 12-W fuel cell designed for use in remote conditions, such as when camping, in boats, for military applications and for remote communications, and is shown in Figure 4.26. The electrodes are in the form of a disc or ring, as in Figure 4.27. The... 

The complexity of the overall fuel processing system for carbonaceous fuels indicates the challenge associated with adapting conventional fuels for use in small fuel cell systems. Considerable effort is required in designing and optimizing the system to achieve the requisite miniaturization and low cost in these applications. 

In another study by Wu et al. (2005), the optimal operating conditions based on validated multiresolution fuel cell simulation tool has been developed with four control parameters including cell temperature, cathode stoichiometry, pressure, and humidity. The study shows that different optimal solutions exist for different system assumptions, as well as different current loading levels, classified into small, medium, and large current densities. This design can be readily applied to a larger number of control parameters and further to the fuel cell design optimizations. 

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